1. Field of the Invention
The present invention relates generally to alkali metal ion batteries, and, more particularly, to electrode materials for alkali metal ion batteries.
2. Brief Description of Related Art
Rechargeable metal-ion or "rocking-chair" batteries have been proposed for use in numerous fields. In a conventional metal-ion battery, an insertion compound having an open molecular structure capable of accepting and releasing metal ions is used as an electrode material. In addition to accepting and releasing metal ions, the electrode material must also be capable of accepting and releasing electrons, and must be able to exist in more than one stable oxidation state. Furthermore, for most commercial purposes, the electrode material must possess all of the above qualities at temperatures and under conditions at which battery power supplies are typically used. That is, the electrode material must operate effectively at and near room temperature and pressure. Furthermore, the electrode material must be able to operate under conditions to which, for example, portable electronic equipment might be exposed.
The amount of energy which can be released by the electrode material is dependent upon the number of metal ions and electrons which can be accepted and released by the electrode material. A particular difficulty associated with metal-ion batteries is achieving sufficient energy output from the electrode materials. For example, compounds such as LiMn.sub.2 O.sub.4, LiCoO.sub.2, and LiNiO.sub.2, which are currently being used in lithium metal-ion batteries, have an energy output or "specific capacity" of under 200 milli-Ampere hours per gram (mAhr/g).
Thus, a need exists for a compound which has an open molecular structure capable of accepting and releasing metal ions, which is able to accept and release electrons, which is able to exist in more than one stable oxidation state at temperatures and under conditions at which battery power supplies are typically used, and which provides an energy output or specific capacity greater than that of compounds currently being used in metal-ion batteries.